1. Field of the Invention
This invention relates to the field of metal part fabrication, and particularly to the direct metal fabrication of parts with surface features only.
2. Description of the Related Art
Many techniques have been developed for fabricating metal parts. Some parts, such as metal stamping dies, have surface features only; i.e., with no re-entrant angles at the part""s side faces. Historically, such parts have been machined by removing material from a block to form a final part. However, machining is both time-consuming and expensive, and is rarely cost efficient when done on a production scale. More typically, large scale production uses a casting process that is fairly time and cost efficient and produces cast quality final parts. However, the cost of retooling and machining a new part can be very high, both in dollar and man hour investment, and in the delay in getting a new design into production. This can be a significant deterrent to updating and improving the design of the part.
Alternatives to machining and casting have been developed in recent years. U.S. Pat. No. 5,745,834 to Bampton et al. and assigned to Rockwell International, the Assignee of the present invention, uses a powder blend of a parent metal alloy X such as Haynes 230, a metal alloy Y that is identical to alloy X except that it is doped with another alloying element such as boron to lower its melting point, and a polymer binder. A thin layer of the powder blend is spread on a table, and a green form part is built up layer-by-layer by localized laser melting of the polymer binder; computer aided design (CAD) data is typically used to control the laser. The polymer binder is eliminated from the green part by heating in either a vacuum furnace or a furnace with an inert environment. Densification is performed at a temperature above the melting point of the lower temperature alloy, but below the melting point of the base metal alloy, to produce transient liquid sintering to near full density.
Though effective for the fabrication of three-dimensional metal parts, the method described in Bampton requires a considerable amount of complex equipment, which may be prohibitively expensive for the manufacture of simpler metal parts with surface features only.
A method of directly fabricating metal parts with surface features only is presented, which is simpler, quicker and less expensive than previously-known methods such as those described above.
A mold is made of a metal part having surface features only. A powder blend is poured into the mold, which includes a base metal, a lower melting temperature alloy of the base metal, and a polymer binder. The mold containing the powder blend is heated until the polymer binder melts and adheres the metal particles to form a green part. The green part is removed from the mold and placed in a crucible, and loose ceramic powder is packed around the part to support it. The supported green part is then heated as needed to vaporize the binder and consolidate the part via liquid phase sintering. The mold is scaled to account for the consolidation of the part. Once cool, the consolidated part can be machined to meet precise dimensional tolerances, if necessary.
The described method enables a surface-feature-only metal part to be directly fabricated in hours, rather than days or weeks. The scaled mold can be repeatedly re-used to produce additional parts if needed. No complex laser equipment is required, nor must each part be individually machined. Despite the expediency of the novel process, the finished part is tough enough to serve as, for example, a metal stamping die (after appropriate heat treatment to enhance hardness) or an electrical discharge machining (EDM) electrode.
Further features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.